In a field of telecommunication, a copper cable has been and is being replaced with an optical fiber cable so as to greatly increase an amount of information to be transmitted per unit cross sectional area of the cable. However, it is still desired to further increase the amount of information to be transmitted per unit cross sectional area of the optical fiber cable. To this end, there has been proposed a bunched optical fiber having plural cores therein.
Conventionally, the bunched optical fiber is produced by inserting a bundle of plural glass rods which form cores and claddings in a glass tube, heating and melting a composite of the glass rods and the glass tube to integrate them together and drawing it to fabricate the bunched optical fiber. However, the conventional bunched optical fiber has very poor dimensional accuracy. For example, the positions of the cores are not accurate and/or the cross section of each core is out of round.